reset mysql password https://help.ubuntu.com/community/MysqlPasswordReset
set new pass:
mysqladmin -u root password newpass
---------------------
change pass:
mysqladmin -u root -p oldpassword newpass
---------------------
sudo service mysql stop
sudo mysqld --skip-grant-tables --user=root
UPDATE mysql.user SET Password=PASSWORD('<новый пароль>') WHERE User='root';
FLUSH PRIVILEGES;